The present invention relates to end fittings for connection to pipes (or other at least partly tubular objects), especially polyethylene and other plastic pipes. It particularly relates to towing heads and pressure test sets.
Towing heads may be useful in pipe laying and in directional drilling. For example, a hole for a pipe may be produced, e.g. under a road, by means of a drill string. This is then connected to a reamer and pipe and drawn back.
High pressure mud is pumped down the drill string and through the reamer during the drilling and reaming operations.
The reamer enlarges the hole to accommodate the pipe. However in the process the pipe is subject to considerable stresses. It risks being damaged or detached. Even if neither of these happens, mud may be forced into its interior, necessitating cleaning before use, especially if it is for use as a water supply pipe, gas pipe, or fibre optic duct.
Each polyethylene pipe of a particular outside diameter may be manufactured with a range of wall thicknesses, depending on the application, resulting in a range of internal diameters. Generally, the outside diameter of the pipe is carefully controlled in the manufacturing process, and a manufacturing tolerance applied to the wall thickness, resulting, again in a variation of internal diameter. It would therefore appear to be simpler technically to design a towing head to seal on the outside, tightly controlled diameter of the pipe than the inside, variable diameter. There are, however difficulties associated with sealing on the outside which become apparent when the four varieties of xe2x80x9cexpandingxe2x80x9d towing head are considered.
A standard, (non pressure-tight) towing head employs a threaded shaft with a towing eye at one end. The shaft passes through an expandable element, and engages a tapered expansion mandrel. In use, a pine is passed onto the head so as to surround the expandable element. Rotation of the shaft draws the mandrel further into the expandable element, causing it to expand radially and grip the bore of the pipe. The pipe-engaging surface of the expandable element has annular ribs of sawtooth section for gripping the pipe. Thus a strong connection can be attained quite easily. This is generally sufficient for a normal pipe laying process. But when very high forces are involved, e.g. in a directional drilling process, it may not suffice. The mandrel can be drawn up further to apply greater force to the pipe, but this increases the risk of splitting the pipe as the pipe continues to expand until the shoulder on the tail of the device impinges the rear of the expanding elements.
A known pressure-tight towing head, which was designed originally to facilitate pressure testing of installed pipe in addition to its use as a towing device, differs from the standard towing head in having a modified tail which is drawn into a separate expander by rotating the eyebolt. The relative axial motion of the tail and expander causes an xe2x80x98Oxe2x80x99 ring to expand radially outwards and seal on the pipe. However, there are two problems associated with this style of towing head. Firstly, the limited movement of the sealing xe2x80x98Oxe2x80x99 ring precludes the use of the same device on more than one wall thickness of pipe. Secondly, as the expanding elements engage the plastic pipe it expands outwards tending to lift off the xe2x80x98Oxe2x80x99 ring and causing the seal to be lost.
A known directional drilling towing head has an annular skirt surrounding and spaced from the expandable element. Generally, the diameter of the expandable element in a non-expanded state will be less than the internal diameter of the skirt (at least at a rear portions and at least in part less than the internal diameter of a pipe to be engaged. Thus a pipe can be engaged over at least part of the expandable element whose subsequent expansion causes the pipe to be engaged between the element and the skirt.
Preferably the skirt has sealing means on its radially inner surface for sealing to a pipe. Since the external diameters of pipes are normally accurately controlled in manufacture, this leads to reliable sealing. A single end fitting is suitable for use with a range of pipes with different internal diameters.
Generally the expandable element has radial projections such as circumferentially extending ribs (e.g. complete or partial annular ribs) that engage the pipe as it expands. Since the rearward ribs tend to be forced more strongly against a pipe than the forward ones, a rearward rib may be shaped and/or dimensioned so as to be less inclined to cut into a pipe.
The end fitting may be a towing head, in which case the elongate element may be a threaded bolt, typically having an engagement formation such as an eye at its front end. A towing head""s body normally has a tapered front portion. There may be separate front and skirt portions. They may be connected by a screw-threaded connection. Of course the handedness of the thread should be such that the parts do not tend to become unscrewed in use.
There are two problems associated with this style of towing head. Firstly, of necessity, the internal diameter of the sealing xe2x80x98Oxe2x80x99 rings positioned in thee outer sleeve is less than the outside diameter of the polyethylene pipe. Thus it is difficult to engage the sleeve over the end of the pipe, especially if the pipe has been coiled and its end is oval. Secondly, if the skirt is of sufficient wall thickness to accommodate the sealing rings, this adds significantly to the effective diameter of the pipe. In some circumstances, this may necessitate an increase in the size of the drilled and reamed hole. Furthermore, the square shoulder generally present on the rear of the skirt may foul obstacles if the pipe has to be pulled back out.
A second variety of directional drilling towing head which facilitates the engagement of the outer sleeve over the end of the pipe has an outer skirt made up of a body and a threadedly engaged operating ring. A xe2x80x98Oxe2x80x99 ring, the internal diameter of which is, at rest, larger than the outside diameter of the pipe, is compressed onto the pipe by rotating the operating ring relative to the body, However, the radial thickness of the operating ring is even more significant than the wall thickness of the fixed xe2x80x98Oxe2x80x99 ring variety and can create great problems if extraction of the pipe becomes necessary.
Increasingly, utility companies co-operate in the installation of ducts and pipes such that large numbers, often of different sizes and for different purposes, are ganged up and, in one operation, are pulled into a single reamed hole. Under these circumstances, outside sleeves reduce the number of ducts which can be ganged, which is another reason why the outside diameter of the sleeve should be kept to a minimum. xe2x80x9cGanging upxe2x80x9d is achieved using a xe2x80x9cmulti duct pullerxe2x80x9d, together with any variety of towing head. Increasingly, the ingress of bentonite (drilling mud) and debris is becoming a serious problem in both gas and fibre optics as well as in water pipe installations.
The design of equipment to pull in ducts, either singly or in multiples must address at least some of the following:
1) Outside diameter of outside sleeve to be kept small.
2) The insertion and locking of the pipe into the device must be simple to achieve and without stress or danger to the operative.
3) Maximum number of ducts or pipes (from 1 upwards) must be accommodated in the minimum cross sectional area.
4) Must be resistant to the ingress of bentonite and debris.
5) Must accommodate a range of specified wall thicknesses and manufacturing tolerances.
Preferred embodiments of the device described hereafter satisfy all or some of these five criteria.
According to the present invention, there is provided an end fitting or a tubular element (particularly a pipe) comprising;
a cup-form body having a base portion and a skirt portion, the base portion having an axial aperture;
an annular sealing assembly which, in use, is within said skirt portion adjacent said base portion;
radially expandable pipe gripping means which are, in use, at least partly within said skirt portion;
expansion means axially displaceable towards the base portion to urge expansion of said pipe gripping means; and
an elongate element extending through said axial aperture, sealing assembly and the pipe fitting means and being coupled to said expansion means;
wherein said annular sealing assembly comprises: a first annular body; a first sealing ring surrounding said first annular body; a second annular body which is axially displaceable relative to said first annular body; the arrangement being such that relative axial displacement in one sense urges radial expansion of said first sealing ring; and a second sealing ring for sealing the sealing assembly to the body.
Preferably the first annular body has a first cylinder portion on which the first sealing ring is mounted, and an enlarged end portion; and the second annular body comprises a collar portion which embraces the cylinder portion; and said collar portion and said enlarged end portion are arranged to engage the first sealing ring and at least one of them is formed with an expander surface such that relative axial movement urges expansion of the first sealing ring.
In one type of embodiment there is also a third annular body which is axially displaceable relative to the second annular body to urge radial expansion of the second sealing ring. The second or third annular body may provide a second cylinder portion on which the second sealing ring is mounted, and an enlarged end portion, said second or third cylinder portion being embraced by a collar portion of the other one of the said second and third annular bodies, the collar portion and enlarged end being arranged to engage and expand the second sealing ring. Preferably the first and second cylinder portions are of different diameters and the sealing assembly is reversible. Thus either sealing ring can seal to a pipe while the other one seals to a respective interior annular surface provided by the skirt portion of the body.
The elongate element may be a screw bolt, particularly when the end fitting is a pipe towing head. It may then be coupled to a threaded bore of the expansion means so that rotation of the bolt draws the expansion means towards the base portion of the body, thus urging expansion of the pipe gripping means and urging axial displacement of the annular bodies of the sealing assembly to urge radial expansion of the first (and in some embodiments the second) sealing ring.
The elongate element may be a tubular element, e.g. if the end fitting is a pressure test end. The elongate element may be fast with the expansion means.
A multiple connection unit may provide end fittings for two or more tubular elements.
In further aspects the invention provides a method of connecting an end fitting to a tubular element, and a process of pipe laying or directional drilling employing an end fitting as defined above. By sealing on the inside of the pipe (only) the outside diameter of the sleeve may be kept to a minimum. The annular sealing assembly or sealing cartridge accommodates a range of wall thicknesses, particularly when reversible. The expanding xe2x80x98Oxe2x80x99 ring principle ensures ease of installation. A multiple connection circuit may employ a geometric layout of the docking ports to ensure that the maximum number of ducts can be accommodated in the minimum area.
Generally, the diameter of both the expandable pipe gripping means in a non-expanded state and the annular sealing assembly will be less than the internal diameter of the skirt (at least at a rear portion) and at least in part less than the internal diameter of a pipe to be engaged. Thus a pipe can be engaged over at least part of the expandable pipe gripping means whose subsequent expansion causes the pipe to be engaged between the gripping means and the skirt, and over the sealing assembly whose subsequent compression causes expansion of the first sealing ring, which seals the pipe.
Generally the expandable pipe gripping means has radial projections such as circumferentially extending ribs (e.g. complete or partial annular ribs) that engage the pipe as it expands. Since the rearward ribs tend to be forced more strongly against a pipe than the forward ones, a rearward rib may be shaped and/or dimensioned so as to be less inclined to cut into a pipe. The pipe gripping means generally comprise a plurality of part-cylindrical shells.
The end fitting may be a towing head, in which case the elongate element may be threaded bolt, typically having an engagement formation such as an eye at its front end. A towing head""s body normally has a tapered front portion. There may be a separate front and skirt portions. They may be connected by a screw-threaded connection. Of course the handedness of the thread should be such that the parts do not tend to become unscrewed in use.
If more than one duct is to be installed at the same time, then a body having multiple docking ports may be used. Each docking port may contain an elongate element, an expandable pipe gripping means, an annular sealing assembly and an expansion means as in the single duct variety. Each is operated in exactly the same way as for a single duct puller. A mud tight nose is then assembled to the front of the body and is secured by the eyebolt which is also used to apply the pulling force to the device.
The invention will now be described in more detail, by way of example, with reference to the accompanying drawings.